1. Field of the Invention
This invention relates to a film feeding or advancing system of a camera and more in particular to a film feeding system of a camera of the type in which upon loading of a film cartridge into the camera, the film inside the cartridge is first wound up to a take-up spool of the camera and then the film is rewound into the cartridge frame by frame after each photographic operation.
2. Description of the Prior Art
Most widely used present day cameras are adapted to use a 35 mm film strip contained in a cartridge in the form of a roll. In order to set such a film cartridge into a camera, the cartridge is placed into the cartridge receiving chamber of the camera body and the leading portion of the film is inserted into the slot of a winding spool which is then rotated to have the leading portion of the film temporarily gripped by the spool. Thus, unexposed frames are contained in the cartridge and the film is wound to the spool frame by frame after each photographic operation. Accordingly, the film portion having exposed frames is wound around the spool and this continues until the frame is used. Upon using all the frames, the film is rewound into the cartridge, which is then removed from the camera for further processing such as developing and printing.
The above-described prior art film feeding system has various disadvantages. First, since the exposed portion of the film is wound to the spool, the photographed images could be destroyed if the back cover of a camera is accidentally opened before rewinding into the cartridge. Second, such prior art cameras are usually provided with a counter which indicates the number of frames used, or pictures taken. This is disadvantageous because the user has to remember the number of remaining exposures since there are several film cartridges in the market which have different numbers of exposures. In order to cope with this problem, there has been proposed a camera provided with a device for indicating the number of remaining exposures. Such a device, however, requires to be set to the maximum number of exposures rated for the film cartridge before use. Thus, such a device is of no use if the operator has forgotten such initial setting.
A third disadvantage of the prior art film feeding system is that after the use of the final frame, the operator might try to forcibly wind the film to the spool so that the perforations provided along both sides of the film could be damaged or the film itself could be torn away in the worst case. If that happens, the film having photographed frames cannot be rewound into the cartridge and thus at least some pictures, which might include a valuable one, will be lost.